Ancient Whale Gave Birth on Land

Feb. 4, 2009 -- A rare fossil of an ancient whale with a fetus still inside reveals that its species -- an ancestor to modern whales -- gave birth on land 47.5 million years ago, according to a paper published in the online journal PLoS.
The discovery, along with prior fossil finds, suggests the first whale ancestors were full-time land dwellers that might have been related to the early relatives of hoofed animals, such as sheep and cattle.
Maiacetus inuus, meaning "mother whale," represents an intermediate evolutionary stage. It lived at the land-sea interface and often moved back and forth between the two environments in what is Pakistan today.
It looked like an improbable cross between a cow, whale, shark, alligator and sea lion.

"Maiacetus was a long-snouted, short-haired mammal with short limbs, webbed hands and feet retaining small hooves on some fingers and toes, and it had a thick, long tail," lead author Philip Gingerich told Discovery News.
Gingerich, a University of Michigan paleontologist, added that the whale "was a foot-powered swimmer and probably lived like a sea lion, spending part of the day or night resting on land and part of the day or night searching for food in the sea."
The fetus was positioned for a "head-first" delivery like land animals, but unlike modern whales. This provides the biggest clue that the species gave birth on land.
The fetus also had a well-developed set of teeth, suggesting it "would be able to get up and move shortly after birth, probably having to keep up with its mother, learning to feed and escape predators," Gingerich said, adding that it would've had to defend itself against very large sharks.

He and his colleagues were stunned to find such a rare fossil, the first ever of its kind.
"To be honest, I never expected to be able to find a whale about to give birth," he said. They also found an 8.5-foot male of the same species at the site.
Since the male whale was only moderately larger than the female, the researchers suspect males of this species didn't control territories or command harems.
Ewan Fordyce, head of the Department of Geology at the University of Osago in New Zealand, told Discovery News, "The convincing presence of a fetus makes this a most important find."
"Fetuses are rarely reported for fossil land mammals," he explained, "and as far as I know, this is the first such case for a whale or, for that matter, any fossil marine mammal."
Fordyce added that the findings are timely, given the forthcoming 200th anniversary of British naturalist Charles Darwin's birth, which occurred on February 12, 1809.
"Darwin would have reveled in such evidence for a major shift in the fossil record," Fordyce explained, referring to the whale's dramatic transition from land to sea.

Theyve speculated that the amblyoceotus ("walking hwale) ancestor was like a transition of an animal that was sort of like a capybara and gradually began to have a shape like an otter (except with little hoofies).
The fact that this specimen was found in PAkistan is like a "Whale central" for most proto whale specimens (from amblyocetus to pacheocetus to basilosaurus [A misnomer but the name change for the original "zeuglodont"])

Here's one to start with...
It's a crocodile feeding strategy employed by a mammal. Easy to see how this would be very functional. Surprising more mammals didn't take this path. Perhaps Ambulocetus was so good at it that others couldn't compete and were blocked.

Crocodiles are limited to warmer waters. I wonder if Ambulocetus filled the colder niches where crocs weren't plentiful. Can you imagine creatures like this, inhabiting northern lakes and ponds, just waiting for something to come to the shore for a drink? The biggest thing we see in ponds around here now are beavers.

Took you long enough to get another picture. I cant believe the dentition though. Those molars are like croc teeth

Given the similar lifestyles and hunting styles, it's interesting that mammals continued to evolve into Cetaceans while Crocodiles barely changed a bit. Makes me wonder why crocodilians never evolved into whale-sized tail driven flippered "crocotaceans". Perhaps being warm blooded and bearing live young gave mammals the flexibility to express new variations whereas crocs were limited by their innate physiology.

whales were caught in the act of adapting to a shallow marine environment while crocs were already "In place".

But we might still wonder why crocs stayed "in place" for all those millennia instead of evolving into larger sea-going highly specialized sea-creatures. I'm guessing it had to do with their basic physiology and their reproductive needs. Crocs are cold blooded and they lay eggs, so the same path to ocean going specialization wasn't open to them (as it was for mammals).

One of the hard parts for mammals would have been the transition from land birth to ocean birth. Modern pinnipeds all give birth on land as do otters and sea lions. I would speculate that the transition to ocean birth involved lots of mothers floating around on their backs with calf on the stomach. Then as the transition became more complete the mothers began to push their babies to the surface the way modern whales do.

Just speculation on my part of course. I know of no way to discover the birthing process transition, since behaviors don't fossilize.

Crocodiles do come in a salt-water version, and rather alligators of certain species and caimans--i do recall having read that they all have a "salt gland" in their mouths, and can tolerate salt water.

Like most reptiles, they lay larges clutches of eggs, but which they then bury and abandon. That may be the significant difference between them and the cetaceans. It may have been more efficient for early cetaceans, still dwelling partly on land, to resort more and more often to the water in order to successfully rear their young, and that simply lead them more and more into deeper water and into living in the water. There would be no such impetus among the crocodiles, alligators and caimans.

But we might still wonder why crocs stayed "in place" for all those millennia instead of evolving into larger sea-going highly specialized sea-creatures. I'm guessing it had to do with their basic physiology and their reproductive needs. Crocs are cold blooded and they lay eggs, so the same path to ocean going specialization wasn't open to them (as it was for mammals).

There were some early Cenozoic
"Thalatts" (seagoing crocs).crocs that were quite a bit larger than the alligators,gavials , caymans, crocs and saltwater crocs of today. The overall body plans of these "Archosaurs" were established well in the MEsozoic and were pretty much unchanged since (with the exception of the budding off of separate sub orders like gavials and caymans).

The ambuloceotans were animals that quickly adapted to a continually rising sea state along a warm water flat lying terrain (The paleoecologists theorize tat the area where the coetaceans developed [the area around present day Pakistan) was then very similar to the Mississippi delta area. It had lots of interconnected stream distributaries to which these animals adapted rather quickly. AND, there were quite a few different species so the "toolbox" of aniumals upon which to fiddle was large enough that the whole shebang didnt go extinct first,

RULE ! :To successfully evolve, its better to have many species of a genus than just one.

0 Replies

farmerman

1

Reply
Wed 7 Oct, 2009 07:56 am

@Setanta,

Quote:

Like most reptiles, they lay larges clutches of eggs, but which they then bury and abandon

The "maian" behavior of alligators and crocs has been studied and recent findings have shown that they are fairly decent parents. They assist in the gestation of their eggs by standing guard and then they help by digging up the eggs. The mothers then hang with the babies for an extended period of time before the babies just swim into the shallows. This habit was studied in Australian and Floridian crocs.